Accessory function of human tumor cell lines I Production of interleukin 1 by the human histiocytic lymphoma cell line U‐937

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Abstract
The established human histiocytic lymphoma cell line U‐937 spontaneously produced a factor with biological activity similar to that ascribed to interleukin 1 (IL1). Actually, supernatants from U‐937 cells promoted proliferation of thymocytes initiated by concanavalin A (Con A) and replaced the requirement of accessory cells for activation of highly purified circulating T lymphocytes induced by Con A. Phorbol myristate acetate (PMA) significantly increased the titers of the helper factor produced by U‐937 cells as compared to that secreted by non‐PMA‐treated U‐937 cells or PMA‐stimulated P388D1 murine macrophage tumor cells. Generally U‐937 cells did not secrete detectable IL1 activity during the first 24‐48 h of culture. However, after this initial period the level of IL 1 activity increased and reached a maximum at 5‐6 days of culture. Finally, the helper factor released by U‐937 cells had an apparent mol. wt. of 12000‐15000 as determined by Sephadex G‐100 chromatography and lacked interleukin 2 activity as shown by its inability to support growth of IL 2‐addicted T cell lines. To our knowledge this is the first report of an established human cell line capable of producing ILL 1.
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